The present invention relates generally to static electricity in vehicles, and specifically to reduction of static electricity buildup in moving vehicles insulated from the surface on which they are traveling.
A build-up of static electricity on a conducting body of a moving vehicle, insulated from the ground, typically occurs in low humidity conditions. The build-up typically manifests itself when an occupant of the vehicle, in exiting the vehicle, touches the body of the vehicle. Charge from the conducting body is then transferred to the occupant, causing the latter to feel an electric shock which may range from a mildly unpleasant sensation to a relatively painful one.
There is a large amount of prior art concerning the reduction of static electricity generated in moving vehicles which are insulated from the ground. In an early example of the prior art, U.S. Pat. No. 907,104 to Brower describes apparatus and a method for removing static electricity from a vehicle, by electrically coupling a conducting portion of the vehicle to the ground. The coupling is performed by connecting a flexible conductor, such as a metal chain, between the conducting portion and the ground.
FIG. 1 is a schematic diagram of apparatus, for removal of static electricity from a vehicle 16, as is known in the art. A wheel 10, typically comprising a rubber tire 12, insulates a conducting body 14 of vehicle 16 from ground 18 on which the vehicle is travelling. As vehicle 16 moves, tire 12 rotates and charge separation occurs in the region where the tire contacts the ground. As is known in the art, the charge separation is significant in low humidity conditions, where the tire and the ground are relatively good insulators. The charge separation generates a static electricity charge on the circumference of the tire, and an opposite charge is generated at the same time on the ground. Depending on the conductive properties of the ground, the charge on the ground dissipates more or less rapidly. The tire rotates and the charge on the circumference of the tire is transferred to conducting body 14. The transfer occurs preferentially, as is known in the art, by charge leakage from the circumference to sharp edges or points of body 14 which are relatively close to the circumference of the tire. The transfer is facilitated by general air movement from the circumference to body 14.
Attached to body 14 is an electrical conductor 19 which electrically connects the body to ground 18 by touching both the body and the ground. Typically conductor 19 is positioned at the rear of body 14. The charge is generated on body 14, as described above, then leaks from the body to the ground via conductor 19.
Unfortunately, if conductor 19 comprises a chain, the chain is not always in contact with the ground as vehicle 16 travels. Also, bottom links of the chain may break off. If conductor 19 comprises a conducting strap, the strap tends to be permanently bent by air pressure so that it does not contact the ground. Although conductor 19 may still facilitate leakage of charge to ground even if it does not touch the ground, by leakage from its end close to the ground, its efficiency is reduced. Especially in low humidity conditions, the effective conductivity of the ground may be relatively low, so that even if conductor 19 does contact the ground, the rate of dissipation of charge from body 14 is also low. Prior art methods have attempted to overcome these and other problems in the system illustrated in FIG. 1. For example, U.S. Pat. No. 2,318,340 to Thacher et al., whose disclosure is incorporated herein by reference, describes a conducting strap which does not contact the ground until a moving vehicle comes to rest. However, in practice, static charge does build up on moving vehicles, and continues to be a problem when the vehicles have stopped, notwithstanding systems known in the art for reducing or eliminating the charge.
It is an object of some aspects of the present invention to provide a method and apparatus for reducing the build-up of static charge on vehicles moving on insulated wheels.
In preferred embodiments of the present invention, a conductor, most preferably in the form of a conducting strip, is attached by an insulator to a body of a vehicle, so that there is substantially no electrical conduction between the conductor and the body of the vehicle. The vehicle is supported on insulated wheels, typically each wheel having a corresponding rubber tire. The conductor is positioned in proximity to one of the wheels, most preferably between a circumference of the wheel and the body of the vehicle. An upper end of the strip is positioned close to, or touches, the circumference of the wheel, and a lower end of the strip is positioned close to, or touches, a surface on which the wheel is traveling. Most preferably, the upper and lower ends of the strip respectively comprise one or more sharp points or edges. Most preferably, a conducting strip as described hereinabove is positioned between each of the vehicle""s wheels and the body of the vehicle.
As the vehicle travels, charge is generated on the circumference of the wheels as described in the Background of the Invention. The charge is removed from the wheels by the upper end of the conductor before it can be transferred to the body of the vehicle, and the charge is transferred to the surface on which the wheel is traveling by the lower end of the conductor. The transfer at the lower end of the conductor is facilitated by the lower end being relatively close to the wheel and to the surface which, especially in low humidity conditions and/or with low surface conductivity, comprises opposite charges to the charge generated. Thus, unlike systems known in the art, the charge generated by the friction of the wheels is returned to the surface on which the wheel is traveling before being allowed to charge the body of the vehicle.
In some preferred embodiments of the present invention, the insulator comprises a mud-flap which is fixedly connected by one side of the mud-flap to the body of the vehicle. The connecting strip is fixedly connected to a second side of the mud-flap. In some preferred embodiments, the connecting strip is retrofitted to an existing mud-flap. In some preferred embodiments of the present invention, the mud-flap comprises an anti-back-splash covering, and the conductor comprises at least part of the covering.
There is therefore provided, in accordance with a preferred embodiment of the present invention, apparatus for preventing electric charge accumulating on a body of a vehicle having a wheel for traveling on a surface, the apparatus including:
an insulator, adapted to be coupled to the body in a vicinity of the wheel; and
a conductor, having an upper end and a lower end, the conductor being coupled to the insulator so that when the insulator is coupled to the body, the upper end of the conductor is held in proximity to the wheel, while the lower end of the conductor is in proximity to the surface on which the wheel travels, and the conductor is electrically insulated by the insulator from the body.
Preferably, the wheel includes a circumference of the wheel, and the conductor is held in proximity to the circumference.
Preferably, the conductor is positioned between the circumference and the body of the vehicle.
Preferably, at least a part of the upper end of the conductor touches the wheel.
Alternatively or additionally, at least a part of the lower part of the conductor touches the surface.
Preferably, the conductor is positioned behind the wheel.
Further preferably, the conductor is positioned behind the wheel relative to a forward direction of travel of the vehicle.
Preferably, at least one of the upper end and the lower end of the conductor include one or more sharp points.
Alternatively or additionally, at least one of the upper end and the lower end of the conductor include one or more sharp edges.
Preferably, the conductor includes one or more sharp points held in proximity to the wheel and intermediate the upper and lower end of the conductor.
Preferably, the insulator includes a mud-flap.
Further preferably, the mud-flap includes an anti-back-splash covering, and the conductor includes at least a part of the anti-back-splash covering.
Preferably, the mud-flap includes an existing mud-flap, and the conductor is retrofitted to the existing mud-flap.
Preferably the apparatus includes a secondary conductor having a secondary upper end and a secondary lower end, wherein the upper secondary end is electrically coupled to the body and the lower secondary end is in proximity to the surface.
Further preferably, the secondary conductor is coupled to the insulator and is electrically insulated from the conductor thereby.
Preferably, the lower end of the conductor is in proximity to the wheel.
There is further provided, according to a preferred embodiment of the present invention, a method for preventing electric charge accumulating on a body of a vehicle having a wheel for traveling on a surface, including:
coupling an insulator to the body of the vehicle in a vicinity of the wheel; and
coupling a conductor having an upper end and a lower end to the insulator so that when the insulator is coupled to the body, the upper end of the conductor is held in proximity to the wheel, while the lower end of the conductor is in proximity to the surface on which the wheel travels, and the conductor is electrically insulated by the insulator from the body.
Preferably, the wheel includes a circumference of the wheel, and coupling the conductor includes holding the conductor in proximity to the circumference.
Further preferably, coupling the conductor includes positioning the conductor between the circumference and the body of the vehicle.
Preferably, coupling the conductor includes at least a part of the upper end of the conductor touching the wheel.
Alternatively or additionally, coupling the conductor includes at least a part of the lower end of the conductor touching the surface.
Preferably, coupling the conductor includes positioning the conductor behind the wheel.
Further preferably, positioning the conductor behind the wheel includes positioning the conductor behind the wheel relative to a forward direction of travel of the vehicle.
Preferably, at least one of the upper end and the lower end of the conductor include one or more sharp points.
Alternatively or additionally, at least one of the upper end and the lower end of the conductor include one or more sharp edges.
Preferably, the conductor includes one or more sharp points held in proximity to the wheel and intermediate the upper and lower end of the conductor.
Preferably, the insulator includes a mud-flap.
Further preferably, the mud-flap includes an anti-back-splash covering, and the conductor includes at least a part of the anti-back-splash covering.
Further preferably, the mud-flap includes an existing mud-flap, and coupling the conductor includes retrofitting the conductor to the existing mud-flap.
Preferably, the method includes coupling a secondary conductor having a secondary upper end and a secondary lower end so that the upper secondary end is electrically coupled to the body and the lower secondary end is in proximity to the surface.
Alternatively or additionally, coupling the secondary conductor includes coupling the secondary conductor to the insulator so that the secondary conductor is electrically insulated from the conductor.
Preferably, coupling the conductor includes positioning the lower end of the conductor in proximity to the wheel.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, a brief description of which follows.